Centrifuge construction of the prior art can be simply set forth. Referring to FIG. 1, such construction consists of the following:
1. Driving motor M is utilized consisting of an exterior stator 14 and central and driven interior rotor 16, this rotor driving output shaft 18 from the motor; PA1 2. Rotor support shaft H is present having supporting bearing 20 transmitting rotating force from output shaft 18 of driving motor M to both support and rotate prior art centrifuge rotor R.sub.O at male coupling 22; PA1 3. Usually, transmission T is provided between output shaft 18 of driving motor M and rotor support shaft H, this transmission consisting either of a belt and pulley drive or suitable gearing; and, PA1 4. Prior art centrifuge rotor R.sub.O is supported at female coupling 24 matching to male coupling 22 of rotor support shaft H. Prior art centrifuge rotor R.sub.O is cylindrical. As in all centrifuges, sample to be centrifuged is contained in the rotor. Here, sample tubes 26 are provided to hold samples 28 undergoing centrifugation. Alternatively, rotor modification can be present for either batch centrifugation or the continuous circulation of materials to be centrifuged to and from the rotor during centrifugation.
The primary difficulty of the prior art is vibration from the combination of the driving motor M, rotor support shaft H, and prior art centrifuge rotor R.sub.O as the rotor undergoes high speed rotation. A discussion of the types of vibration can be helpful. Rotation ranges of centrifuge rotors can include up to 6,000 rpms for low speed centrifuges, up to 30,000 rpms for high speed centrifuges, and even up to 120,000 rpms for ultra-centrifuges.
Referring further to FIG. 1, rotor support shaft H will be seen to provide a columnar support of prior art centrifuge rotor R.sub.O from supporting bearing 20. Specifically, assume that a rotor imbalance exists. Such would be the case where the center of gravity of the rotor is not co-incident to the spin axis of the rotor. During rotation of such a rotor, rotor support shaft H will be bent in a plane normal to the spin axis of the rotor from supporting bearing 20. This will cause transverse shaft vibration 30. When rotor support shaft H and supporting bearing 20 undergoes stress, accumulated to a sufficient degree, it can cause centrifuge failure.
It is known that if prior art centrifuge rotor R.sub.O has imbalance in a vertical plane, rapid stress reversal in rotor support shaft H can occur. Simply stated, if prior art centrifuge rotor R.sub.O has imbalance in a vertical plane, the rotor bends rotor support shaft H each time the support shaft rotates with shaft stress reversing vibration 32. This shaft stress reversing vibration 32 is transmitted directly through male coupling 22 and female coupling 24 to rotor support shaft H.
Stress reversals on a rapidly rotating shaft accumulate over a relatively short operating lifetime cause premature fatigue failures in the metallic structure of the shaft. When it is remembered that any kind of a failure in a high speed rotating centrifuge shaft is catastrophic--usually causing disintegration of the high speed rotor--such vibrations are to be carefully avoided.
To these vibrational components can be added torsional vibrations between driving motor M and prior art centrifuge rotor R.sub.O. Specifically, driving motor M, either alone or through transmission T, can provide an irregular rotating force to prior art centrifuge rotor R.sub.O. For example, driving motor M can provide an irregular rotating force which contains small torsional accelerations and decelerations. This irregular rotating force can superimpose a torsional vibration upon the high speed rotation of the centrifuge. Typically, central and driven interior rotor 16 of driving motor M torsionally vibrates with respect to prior art centrifuge rotor R.sub.O. This torsional vibration is translated between prior art centrifuge rotor R.sub.O and central and driven interior rotor 16 of driving motor M through male coupling 22 and female coupling 24 to rotor support shaft H, transmission T, output shaft 18. Again, the system undergoes vibrational stress--this time in torsion.
The vibrational modes set forth above are relatively simple to explain, but extremely difficult to eliminate as a practical matter. Specifically, these vibrational modes are usually not confined to a single frequency, but include many frequencies. Further, it is well known that such vibrational frequencies "resonate" at certain "critical" frequencies. For example, a change of a rotor--for example substituting a light rotor for a heavy rotor--can change the critical frequency at which the centrifuge drive vibrates. A centrifuge which does not appreciably vibrate with one rotor, can be found to vibrate excessively with another rotor. Consequently, replacement rotor design can be adversely affected by vibrational considerations.
As a direct result of these vibrational modes and generated forces, it is common for centrifuge manufacturers to retain whole engineering departments for the suppression of such vibrations.
In what follows, a new centrifuge design will be presented which naturally suppresses many of these modes of vibration. Such a centrifuge happens to require as a practical matter the use of a ring shaped composite fiber reinforced centrifuge rotor.
The construction of fiber reinforced centrifuge rotors is well known. Such rotors have light weight combined with resistance to the high stress forces imposed during centrifugation, these forces being generally normal to the plane of the spin axis of the rotor. See for example, Piramoon et al. U.S. Pat. No. 4,738,656 issued Apr. 19, 1988 entitled COMPOSITE MATERIAL ROTOR; Piramoon U.S. Pat. No. 4,781,669 issued Nov. 1, 1988 entitled COMPOSITE MATERIAL CENTRIFUGE ROTOR; Piramoon U.S. Pat. No. 4,790,808 issued Dec. 13, 1988 entitled COMPOSITE MATERIAL CENTRIFUGE ROTOR; Piramoon U.S. Pat. No. 5,057,071 issued Oct. 15, 1991 entitled HYBRID CENTRIFUGE ROTOR; U.S. Pat. No. 5,206,988 issued May 4, 1993 entitled HYBRID ULTRA-CENTRIFUGE ROTOR WITH BALANCING RING AND METHOD OF MANUFACTURE. All of these particular rotors relate to so-called vertical tube rotors, where the tubes containing the sample are aligned parallel to the spin axis of the rotor. For the purposes of understanding the possible constructions of the rotors of this invention, these above listed patents are incorporated herein by reference.
In an International Application published under the Patent Cooperation Treaty on Dec. 23, 1993 entitled FIXED-ANGLE COMPOSITE CENTRIFUGE ROTOR by Malekmadani et al., a fixed angle rotor of which I am the omitted inventor, is described. In that disclosure a fixed angle rotor with oblique windings on a conical exterior was provided. The purpose of the oblique windings is to provide a composite rotor with resistance to the forces of vertical separation generated by sample tubes in fixed angle rotors. Rotors having this configuration have been sold more than one year prior to the filing of this patent application; consequently the rotor described in that publication is prior art to this patent application. For the purposes of understanding the possible constructions of the rotors of this invention, this disclosure is incorporated herein by reference.